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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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166 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1959

Halogen-Containing Gases as Boundary Lubricants for Corrosion-Resistant Alloys at 1200 F

The extreme temperatures anticipated for lubricated parts in advanced flight powerplants dictate the consideration of unconventional methods of lubrication such as solid lubricants and the reactive gases described in the present research. These halogen-containing "reactive" gases such as dichlorodifluoromethane, CF2Cl2, are among the most stable of organic molecules. The high "flash" temperatures generated at the contacting asperities as a result of frictional heat are sufficient to cause local decomposition of the halogen-containing gases. The active atoms thus released (e.g., chlorine) then react with the metal to be lubricated to form halides capable of effective lubrication. The presence of small amounts of a sulfur-containing gas (e.g., 1 percent sulfur hexafluoride, SF6) was found to catalyze the formation of metal halides. Friction and wear studies were made with a hemisphere (3/16-in. rad.) rider sliding in a circumferential path on the flat surface of a rotating disk (2 1/2-in. diam.). The specimens of corrosion-resistant 2 alloys were run in an atmosphere of the various gases with a load of 1200 grams, a sliding velocity of 120 feet per minute, and temperature from 75 to 1200 F. An effective lubricant for ferritic materials (M-1 tool steel) was CF2Cl2, but significant corrosion occurred above 600 F. Corrosion evaluation in CF2Cl2 suggested a number of nickel- and cobalt-base alloys for additional lubrication study. Several combinations of gases and these metals were found to lubricate to 1200 F without excessive corrosion. The gases were CF2Cl2 Plus 1 percent SF6, monobromotrifluoromethane CF3Br plus 1 percent SF6, dibromodifluoromethane CF2Br2, iodotrifluoromethane, CF3I, and I2. Careful selection of metals and gas are necessary for successful lubrication over specific temperature ranges. Optimum combinations give friction coefficients as low as 0.05 without

Buckley, Donald H.↗
DOE OSTI2021

Ultra-High Temperature Thermal Conductivity Measurements of a Reactive Magnesium Manganese Oxide Porous Bed Using a Transient Hot Wire Method

Pelletized magnesium manganese oxide shows promise for high temperature thermochemical energy storage. It can be thermally reduced in the temperature range between 1250 °C and 1500 °C and re-oxidized with air at typical gas-turbine inlet pressures (1–25 bar) in the temperature range between 600 °C and 1500 °C. The combined thermal and chemical volumetric energy density is approximately 2300 MJ/m3. The rate at which a thermochemical storage module can be charged is limited by heat transfer inside the solid packed bed. Hence, the effective thermal conductivity of packed beds of magnesium-manganese oxide pellets is a crucial parameter for engineering Mg-Mn-O redox storage devices. We have measured the effective thermal conductivity of a packed bed of 3.66 ± 0.516 mm sized magnesium manganese oxide (Mn to Mg molar ratio of 1:1) pellets in the temperature range of 300–1400 °C. Since the material is electrically conductive at temperatures above 600 °C, the sheathed transient hot wire method is used for measurements. Raw data is analyzed using the Blackwell solution to extract the bed thermal conductivity. The effective thermal conductivity standard deviation is less than 10% for a minimum of three repeat measurements at each temperature. Experimental results show an increase in the effective thermal conductivity with temperature from 0.50 W/m °C around 300 °C to 1.81 W/m °C close to 1400 °C. We propose a dual porosity model to express the effective thermal conductivity as a function of temperature. This model also considers the effect of radiation within the bed, as this is the dominant heat transfer mode at high temperatures. The proposed model accounts for microscale pellet porosity, macroscale bed porosity, pellet size, solid thermal conductivity (phonon transport), and radiation (photon transport). The coefficient of determination between the proposed model and the experimental results is greater than 0.90.

Engineering↗
DOE OSTI2026

Nuclear Data Impact Assessment for the HTR-10 Pebble-Bed Reactor Using SCALE

The HTR-10 was used as a representative pebble-bed high-temperature gas-cooled reactor in this assessment of nuclear data’s impact on important reactor and spent fuel metrics, including safety-related quantities such as the effective multiplication factor (k eff ), temperature reactivity feedback, spent fuel inventory, and decay heat. Using the SCALE code system tools and ENDF/B-VII.1 nuclear data libraries, we quantify the effect of nuclear data uncertainties on these key performance metrics for both fresh fuel and equilibrium core configurations. For reactor core key parameters, important contributors to uncertainty include reactions of 235 U [$\bar{v}$, fission, (n, γ)], 238 U [elastic, (n, γ)], and graphite [elastic, (n, γ)]. Additional important contributors for the equilibrium core include reactions of higher actinides ( 239 Pu, 240 Pu) and fission products ( 135 Xe, 149 Sm). For spent fuel analysis, most nuclide inventory uncertainties remain below 5%. Higher uncertainties up to 11% are being observed for minor actinides like 243 Am and 244 Cm. Additionally, fission product uncertainties in 155 Eu and 155 Gd, of 25% and 23% respectively, are also significant and have implications for burnup credit applications. 110m Ag also shows high uncertainty of up to 11%, mainly due to fission product yield uncertainties. Decay heat relative uncertainties remain below 0.6% up to 10 years’ cooling time after fuel discharge. The highest relative uncertainty of 1.5% occurs at 500 years of cooling; however, because the decay heat value is very low at that time, the absolute uncertainty is not significant. This work demonstrates that extending assessments beyond fresh fuel k eff to include irradiated cores, nuclide inventories, and decay heat is essential in understanding the behavior of uncertainties as a function of fuel burnup and can support improvements of safety margins and spent fuel management.

Nuclear data impact↗
DOE OSTI2023

Robust highly durable solid oxide fuel cell cathodes – Improved materials compatibility & self-regulating surface chemistry

Solid oxide fuel cells (SOFCs) are electrochemical conversion devices that directly transform hydrogen or hydrocarbon fuels to electricity, with energy efficiencies as high as 90%, coupled with reduced emissions. Several factors, however, remain to be addressed when considering scale-up of SOFC technology, including the need to overcome decreased performance due to sluggish rates of the oxygen reduction reaction (ORR) at the cathode under reduced temperatures and susceptibility to degradation in performance from surface poisoning e.g. from chromia, while limiting the use of critical raw materials (lanthanides and transition metals) present in high performing mixed ionic electronic conducting electrodes like (La,Sr)CoO 3 (LSC). In this project we explored the key descriptors for determining ORR activity in SOFC electrodes and tried to recover performance degradation by applying them to SOFC electrodes. In order to do this, we first selected a model mixed ionic electronic conducting (MIEC) oxide, Pr-doped CeO 2 (Pr 0.1 Ce 0.9 O 2-δ , PCO), which is a chemically stable fluorite and free of inherent poison sources (e.g. Sr segregation in LSC) that potentially react with external impurities such as Cr-species vaporized from the interconnect. The three approaches originally planned in this project are as follows: 1) evaluation of scavenger exsolution characteristics, 2) study of scavengers gettering efficacy following Cr and Si poisoning and 3) integration of new compositions into porous electrodes. Among them, exceptional progress has been made in 2) and 3), especially understanding the role of surface infiltrants in impacting electrode performance and degradation of PCO materials. We found that the Smith acidity scale for binary oxides serves as a powerful descriptor for tuning and predicting the oxygen exchange kinetics on MIEC PCO surfaces. As a result, with infiltration with binary oxides, ranging from strongly basic (Li 2 O) to strongly acidic (SiO 2 ) onto the surface of porous PCO, it was possible to systematically vary the chemical surface exchange coefficient (k chem ) by 6 orders of magnitude! L i2 O increased k chem by nearly 1,000 times over that of pristine PCO, while SiO 2 decreased k chem by nearly the same factor. Strikingly, although the pre-exponential of k chem scales linearly with the acidity of the infiltrated binary oxide, there is nearly no change in the activation energy. With this insight, we attributed the origin of these dramatic changes in k chem values to the systematic increase and decrease in the surface electron density induced by infiltrated binary oxides. More interestingly, although both Cr 2 O 3 and SiO 2 were determined to be acidic by Smith, suggesting that this feature could likely be the primary reason that these compounds serve to poison the ORR on SOFC cathodes, the effect of poisoning could be subsequently tuned by adding multiple infiltrants and controlling their relative surface acidities. We also systematically examined the effect of serial infiltration of basic and acidic oxides. It turned out that serial infiltration of Li not only recovers approximately 20-fold degraded k chem of PCO by acidic Cr 2 O 3 but its k chem is enhanced even beyond that of the non-infiltrated PCO by more than three orders of magnitude. This was further verified with a screen-printing PCO symmetric cell in terms of the electrode performance (area-specific resistance, ASR) related to approach 3). These observations point to acidity as a key descriptor not only in tuning and predicting the ORR activity of SOFC cathodes that largely determines the overall performance of SOFC, but in mitigating and reactivating poisoned electrode performance. This work provides novel guidelines for making the electrode performance much more active and robust in SOFCs, which can further be applied to all applications requiring oxygen exchange reaction, such as electrolyzers, permeation membranes and gas sensors.

30 DIRECT ENERGY CONVERSION↗